Method and arrangement for implementing intra-frame interleaving

ABSTRACT

A method and radio device are provided for interleaving a stream of data ( 201 ) including digital information symbols prior to transmission over a radio interface. A permutation is performed ( 202, 203, 401, 402 ) to the steam of digital data, thus producing a permutated stream of digital data ( 204 ). From the permutated stream of digital data there are provided at least two component streams ( 404 ) for mapping each component stream into a spreading code ( 406 ). The order of information symbols is reversed ( 405 ) in at least one component stream prior to mapping it into a spreading code.

TECHNOLOGICAL FIELD

The invention concerns generally the technology of interleavingtransmission symbols in a radio transceiver in time domain. Especiallythe invention concerns the technology of implementing intra-frameinterleaving in multicode transceivers of the proposed UTRA (UniversalTerrestrial Radio Access) system.

BACKGROUND OF THE INVENTION

The Layer 1 multiplexing and channel coding characteristics of the FDD(Frequency Division Duplex) mode of the UTRA are, at the priority dateof this patent application, defined in the document “TS 25.212 V3.0.0(1999-10), 3rd Generation Partnership Project (3GPP); TechnicalSpecification Group (TSG) Radio Access Network (RAN); Working Group 1(WG1); Multiplexing and channel coding (FDD)” available through the3GPP. FIG. 1 illustrates the transport channel multiplexing structurefor uplink as defined in said document. The functional blocks the serialconnection of which is shown in the upper part of FIG. 1 are CRCattachment 101, transport block concatenation and code blocksegmentation 102, channel coding 103, radio frame equalisation 104,first interleaving 105, radio frame segmentation 106 and rate matching107. Several entities of the above-described kind may be coupled to theinputs of a transport channel multiplexing stage 108, the output ofwhich is further coupled to the serial connection of physical channelsegmentation 109, second interleaving 110 and physical channel mapping111.

In the downlink direction there may be certain modifications to thearrangement of functional blocks shown in FIG. 1, but at least the lowerend of the arrangement which consists of the physical channelsegmentation, second interleaving and physical channel mapping entitiesremains the same. For the purposes of the present invention it sufficesto analyze the operation of the second interleaving and physical channelmapping blocks.

The aim of the second interleaving 110 is to permutate the bits in timedomain so that bits that originally were close to each other in the bitstream to be transmitted are separated from each other in the timedomain for the duration of their travel over the radio interface. Thisway a short interval of extremely bad interference conditions at theradio interface should not cause any bursts of several consecutiveerroneous bits in the received and decoded bit stream. The secondinterleaving 110 takes place in inter-frame manner meaning that the dataentity subjected to interleaving is one radio frame.

FIG. 2 illustrates the operation of the second interleaving stage. Thebits that come as an input stream 201 to the interleaver are writteninto a bit array 202 which has a certain number of rows and a certainnumber of columns. The numbers shown in the input stream and the bitarray are simply the serial numbers of the bits in the radio frame. Herethe number of columns is shown to be 32, with column numbers rangingfrom 0 to 31. The columns are fed into an intercolumn permutator 203which rearranges them into a different order. As examples, the 0thcolumn remains 0th, the 17th column comes 1st, the 14th column comes30th and the 31th column remains 31th after the intercolumn permutator203. The bits are read from the permutated columns to the output of thesecond interleaving stage column by column. The bit stream 204 with theserial number of certain bits is shown as the output of the secondinterleaving stage.

The TDD or Time Division Duplex mode with its possibility ofsimultaneously using several spreading codes brings about somecomplications to the presented arrangement. If a single spreading codeis used to transmit the bit stream, the bit stream 204 is transmitted byusing that spreading code. However, in a multicode situation thetransmitting device has at least two spreading codes at its disposal,and it transmits by using these parallel spreading codes simultaneouslyduring a single time slot. The presently defined physical channelmapping arrangement is such that the parallel spreading codes are filledone at a time with bits taken from the bit stream 204. This may lead tothe situation shown at the bottom of FIG. 2 where, during a certain timeslot, e.g. bits 0 and 14, bits 32 and 46 and so on of a certain frameare transmitted simultaneously. Currently the number of parallelspreading codes may vary between 2 and 9.

The arrangement according to FIG. 2 has the drawback of in the multicodesituation canceling much of the advantages usually obtained through thesecond interleaving, because certain bits that are near to each other inthe frame are practically not separated at all in the time domain at theradio interface. The nature of the interference occurring in UTRAsystems is such that it may occur e.g. that a part of a time slot eitherfrom the very beginning or from the very end of the time slot getserased due to interference, especially inter-operator interference. Theresult of such an erasure, taken the arrangement of FIG. 2, is a burstof errors very close to each other in a received frame.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and anarrangement for ensuring that the separation in time between adjacentbits in a frame does not suffer in a multicode transmission arrangement.It is a further object of the invention that major changes in theexisting proposed arrangements could be avoided.

The objects of the invention are achieved by modifying the order inwhich the bits are mapped into the spreading codes after the secondinterleaving stage.

The method according to the invention is meant for interleaving a streamof data consisting of digital information symbols prior to transmissionover a radio interface. It comprises the steps of

-   -   performing a permutation to the stream of digital data, thus        producing a permutated stream of digital data,    -   producing, from the permutated stream of digital data, at least        two component streams    -   mapping each component stream into a spreading code.        It is characterized in that it comprises the step of reversing        the order of information symbols in at least one component        stream prior to mapping it into a spreading code.

The invention also applies to a transmitter arrangement which comprises

-   -   means for performing a permutation to the stream of digital        data, thus producing a permutated stream of digital data,    -   means for producing, from the permutated stream of digital data,        at least two component streams    -   means for mapping each component stream into a spreading code.        It is characteristic to the radio device that it comprises means        for reversing the order of information symbols in at least one        component stream prior to mapping it into a spreading code.

The present invention is based on a finding that the mapping of bitsinto the parallel spreading codes has a key role in maintaining theseparation of bits in the time domain. An advantageous way to eliminatethe drawbacks of the existing arrangements is to modify the order inwhich the bits are mapped at least to a part of the spreading codes.

In order not to cause major changes into the existing proposedarrangement it was found that if in every second one of the componentbit streams that are parts of the output of the second interleaver theorder of bits is inverted, sufficient separation in time domain betweenbits is maintained. Such a modification contains essentially no addedcomplexity, because the order in which a certain finite bit stream isread (from first bit to last bit or from last bit to first bit) ismerely a question of choosing a certain memory access command properly.

The invention requires only a minor change in the existing proposedarrangements, and yet it provides a significant relief to the problem ofmaintaining sufficient separation in time domain between bits that areclose to each other in the frame.

BRIEF DESCRIPTION OF DRAWINGS

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

FIG. 1 illustrates a known transport channel multiplexing structure foruplink,

FIG. 2 illustrates the results of second interleaving and code mappingin the arrangement of FIG. 1,

FIG. 3 illustrates the results of second interleaving and code mappingaccording to an advantageous embodiment of the invention,

FIG. 4 is a flow diagram of the method according to the invention and

FIG. 5 illustrates a radio device according to an embodiment of theinvention.

FIGS. 1 and 2 were already accounted for in the description of priorart. Like parts in the drawings are shown with the same referencedesignators.

DETAILED DESCRIPTION OF THE INVENTION

The upper part of FIG. 3 is similar to that of FIG. 2: The bits thatcome as an input stream 201 to a second interleaver are written into abit array 202 which has a certain number of rows and a certain number ofcolumns. Here the number of columns is again 32, with column numbersranging from 0 to 31. The columns are fed into an intercolumn permutator203 which rearranges them into a different order. The present inventiondoes not change the operation of the intercolumn permutator, so the 0thcolumn remains 0th, the 17th column comes 1st, the 14th column comes30th and the 31th column remains 31th after the intercolumn permutator203 just as in the prior art arrangement of FIG. 2.

The invention pertains to the order in which the bits are read from thepermutated columns to the output of the second interleaving stage, whichis also the input of the physical channel mapping stage. The bit stream204 with the serial number of certain bits is shown as the known outputform of the second interleaving stage. However, when the bits are mappedtherefrom to the parallel spreading codes of which there are two in FIG.3, the order of bits in the component bit stream that goes into thesecond spreading code is reversed.

The principle shown in FIG. 3 is easily generalized to the case of Nparallel spreading codes, where N is a positive integer greater than 2,by stating that the bit order in every second component bit stream isreversed before mapping that component bit stream into the correspondingspreading code.

The invention does not limit the choice of the actual physical step inwhich the inverting of bit order is made for every second component bitstream. The system specifications of communications systems like theUTRA do not usually specify any particular hardware implementation forperforming the standardized operations, but these are left into thediscretion of transceiver designers. One advantageous way to perform thereversing is to integrate it into the step in which the bits are readfrom the bit array 202 after column permutation: the step of permutatingcolumns does not mean anything else than correctly selecting the orderin which bits are read from the memory locations where they are storedwhen they are said to be in the bit array. The transceiver mayreorganize this reading order that in addition to the permutated orderof columns, it takes into account the fact that those columns that go tothe bit streams destined to be reversed are read in an inverted orderand from bottom to top in the array representation.

FIG. 4 illustrates a method according to an advantageous embodiment ofthe invention in the form of a flow diagram. The steps shown in FIG. 4belong functionally to the second interleaving stage 110 shown in FIG.1. Step 401 corresponds to writing the input bits into a bit array, andstep 402 corresponds to permutating the columns. At step 403 thetransceiver checks the number of spreading codes it has at its disposalfor transmitting this particular frame. If the number of codes is onlyone, the permutated columns are output in the known order so that theycan be correctly mapped into the spreading code at step 406. If,however, there is a positive finding at step 403, component streams are(at least conceptually) composed at step 404 and in every second one ofthese the bit order is reversed at step 405.

FIG. 5 illustrates the structure of a mobile terminal or base stationwhere the parts from the CRC attacher 101 to the physical channelsegmentator 109 may be similar as in known devices that conform to theTS 25.212 document mentioned in the description of prior art. The secondinterleaver 510 and the physical channel mapper 511 together arearranged to implement the method illustrated in FIG. 4; the physicalimplementation of the method is straightforward and within thecapabilities of a person skilled in the art on the basis of theabove-given instructions.

In one embodiment, the radio device comprises means for interleaving astream of data having digital information symbols prior to transmissionover a radio interface, that includes means for performing a permutationto the stream of digital data, thus producing a permutated stream ofdigital data, means for producing, from the permutated stream of digitaldata, at least two component streams, means for reversing the order ofinformation symbol in at least one component stream and means formapping each component stream into a spreading code.

In one embodiment, the radio device is a mobile terminal of a 3GPP radiocommunication system. In another embodiment, the radio device is a basestation of a 3GPP radio communication system.

The above-given exemplary embodiments should not be construed aslimiting the applicability of the invention; the latter is merelyreflected in the scope of the appended claims. For example the inventiondoes not require that an interleaving operation where every secondcomponent stream to be mapped into a spreading code should be limited tointerleaving within a single time slot. Similarly the permutation andorder inverting operations may be performed on groups of bits (e.g. sothat three consecutive bits constitute a group) instead of just bits.

1. A method for interleaving a stream of data consisting of digitalinformation symbols: performing a permutation to the stream of digitaldata, thus producing a permutated stream of digital data, producing,from the permutated stream of digital data, at least two componentstreams, reversing the order of information symbols in at least onecomponent stream and mapping each component stream into a spreading codeused for spread spectrum transmission over a radio interface.
 2. Amethod according to claim 1, comprising the step of reversing the orderof information symbols in every second component stream prior to mappingthese component streams into their corresponding spreading codes.
 3. Amethod according to claim 1, wherein the step of performing apermutation to the stream of digital data comprises the steps of writingthe information symbols of a certain passage of the stream of data intoa permutation matrix and reading the information symbols from thecolumns of said permutation matrix in a column order which is differentthan the order of continuous columns in said permutation matrix; so thatthe steps of producing at leant two component streams and reversing theorder of information symbols in at least one component stream areperformed on a discrete sequence of information symbol obtained as aresult of said reading of the information symbols from the columns ofsaid permutation matrix.
 4. A radio device comprising means forinterleaving a stream of data consisting of digital information symbolsprior to transmission over a radio interface, comprising: a permutatoradapted to perform a permutation to the stream of digital data, thusproducing a permutated stream of digital data, a component streamproducer adapted to produce, from the permutated stream of digital data,at least two component streams, symbols order reverser adapted toreverse the order of information symbol in at least one component streamand a mapper adapted to map each component stream into a spreading codeused for spread spectrum transmission over a radio interface.
 5. A radiodevice according to claim 4, the radio device being a mobile terminal ofa 3GPP radio communication system.
 6. A radio device according to claim4, the radio device being a base station of a 3GPP radio communicationsystem.